In the semiconductor industry, manufacturers scale down the device dimensions to increase the performance as well as reduce the cost of manufacture. The scaling down of devices has led to the development of several new processing techniques. In the manufacture of certain devices, wet etching has been replaced with dry etching (plasma etching, reactive ion etching and ion milling). Low-resistivity suicides and refractory metals are used as replacements for high-resistivity polysilicon interconnections. Multiple-resists have been developed to compensate for wafer surface variations that thwart accurate fine-line lithography.
However, improved lithography processing techniques continue to be the main factor in the ability to scale devices. Improvements have come in, for example, lithographic tools, such as 1:1 optical projection systems fitted with deep-ultraviolet source and optics. Further, new photoresist materials have been introduced. Further still, new processes have been developed, such as a multilayer resist utilizing a top resist sensitized to X-ray or electron-beam and a bottom straight optical resist layer(s).